Shutter speed on F900R

I would ask a something about shutter speed.
In F900R, at 29.97PsF, what is mean that shutter "OFF" ?
As far as I know, in such a case shutter be set 1/30 that it is applied 360 degree shutter speed.
is it right?

In actually, footage is lighter than 1/60 at shutter "OFF".
so I told my DP that "OFF"mode is 1/30, but he didn't agree because 1/30 shutter made much motion blur.
he said shutter OFF mode was shooting 1/48 regardless of frame rates.